The ideas developed in this patent are in the field of the fluorescent materials developed these last years for many applications. The luminescent properties of different materials were developed in many application fields like laser dyes, chemicals stains or biological labeling. Photo-luminescent properties like life time, FRET, polarization fluorescence, multiphotons excitation, phosphorescence or quenching were studied and lead to specific developments that enlarged the number of applications especially in biochemistry, in physics and telecom.
A non exhaustive list of the materials available for the different applications can be: organic dyes, organo-metallic molecules, metallic nanoparticles, rare earth complexes, lanthanides or metallic alloys, used as free molecules or as colloidal dispersions.
Each kind of material has its specificities, its properties and its limitations. Usually the choice of material is conditioned by the application requirements.
The idea here is to propose the most versatile material that should combine most of the advantages coming from the different materials, and that will considerably reduce the known disadvantages, like photostability, chemical stability or no expected biological interactions. In this application, the proposed labelled material, in particular fluorescent material, is based on silica nanoparticles. A lot of literature references are already describing fluorescent silica nanoparticles, but as they used the TEOS (tetraethyl orthosilicate) route, the nanoparticles are porous, which affect the chemical stability and the physical properties. In addition, the TEOS route will never allow the synthesis of particles with less than 15 nm diameter.
Silica nanoparticles were described for the first time by Stöber in 1968, and different patents followed (Unger and al in 1988, Border and al in 1991) to improve the particles synthesis, using the TEOS route. The main improvement was the reduction of porosity (but not fully eliminated), and the reduction of polydispersity. The method was extensively used to encapsulate different materials like organic dyes, inorganic dyes, metallic nanoparticles (iron oxide, ZnO . . . ), and the silica porosity was used as an advantage in silver (or iron oxide) core-silica shell structures, to dissolve the core and obtain hollow silica shells. In our case, this porosity is a real issue for the long term stability of the materials we target.
More recently, new silica based nanoparticles using silicate route were optimized by Persello (1994, then 1999). In this work, Persello demonstrated the capability to produce highly dense nanoparticles of different sizes from 1 nm to few tenths of nm in diameter. The particles are then non porous, and very well defined; the author claims applications in catalysis, and solid support chemistry. In his whole work, the functionalization was done on the surface of the particles, and never in the core. Moreover, he never functionalized his particles with fluorophores.